Big trees generate more seeds, provide more habitat for animals, and help forests resist disturbances. They also store more carbon compared to small trees. A scientific study published in Global Ecology and Biogeography highlights the importance of large trees in sustaining the wildlife and the global climate. These forest giants store up to half the above-ground biomass in tropical forests, playing a critical role in mitigating climate change.
The research involved dozens of scientists from more than 40 institutions, and it is based on data from nearly 200,000 individual trees across 120 lowland rainforest sites in Africa, Asia, and Latin America: big trees, measuring at least 70 cm in diameter at breast height, represent less than 5% of stems, but store up to 50% of tropical forest biomass. The amount of carbon storage varies across tropical forest regions, but is substantial in all natural forests.
African rainforests, with an average of 418 tons of above-ground biomass per hectare, stored the most carbon. Big trees accounted for an average of 44 percent of African forests' biomass. Other research has suggested that the preponderance of large trees in African forests is due to the abundance of large herbivores, which suppress smaller trees.
Asia was second with an average of 393 tons, of which large trees accounted for 154 tons or 39 percent of total above ground carbon. Latin America averaged 288 tons per hectare, about a quarter of which occurred in large trees.
The findings emphasize the importance of big trees, which typically dominate old-growth forests. Big trees also have important ecological functions, offering niche habitats for wildlife and providing abundant fruit, foliage, and flowers.
Yet big trees are particularly at risk due to their attractiveness to loggers, who typically target the largest and oldest trees in selective logging operations. Big trees are also especially vulnerable to ecosystem change, including drought, increased incidence of wildfires, edge effects, and disease.
Several studies suggest that large trees may be vulnerable to changing climate, potentially leading to declining forest biomass storage. This means that when the big trees die, they release back the carbon they store into the atmosphere. As a result, forest erosion, selective logging, drought and forest fires can can transform them into a climate bomb.
The new study adds urgency to calls to better protect old-growth forests for climate stabilization and conservation of biodiversity.